At present the medical fields of gastroenterology, respirology, gynaecology, urology, otorhinolaryngology, dermatology, ophthalmology, cardiology and neurology are concerned.
The use of a flexible optical fibre bundle with a small diameter (several hundred microns) is necessary for coupling with the instrument channel of an endoscope but it can also be advantageous for automatic testing systems in which the optical fibre bundle, with a focusing optical head at its end, is manipulated automatically like a measuring arm on a sample matrix. Moreover, independently of endoscopic use, miniaturization of the optical head is also advantageous for increasing positioning precision and also for minimizing mechanical inertia in automated uses.
More particularly, the equipment according to the invention is of the type comprising a source emitting radiation of a given wavelength producing a parallel illumination beam. This illumination beam is then separated for example by a separating plate in order to split the illumination path and the detection path. It is then deflected angularly in two spatial directions (scanning) by an optomechanical system of mirrors. An optical means then picks up the beam scanned angularly and injects it into an image guide situated in the focal plane of the latter and constituted by an organized bundle of several tens of thousands of flexible optical fibres. Thus, at a given moment, one of the optical fibres of the image guide is injected for a given angular position of the bundle. Over time, the optical fibres constituting the image guide are injected successively, by angular deflection of the beam by means of the mirrors, point-by-point for a given line, and line-by-line in order to constitute the image. The bundle injected into the image guide (if appropriate previously arranged in the instrument channel of an endoscope) is guided, emerges from it and is picked up by an optical means allowing illumination point-by-point of the site which is to be observed. At any moment, the spot illuminating the tissue is backscattered and follows the reverse path of the incident beam. This backscattered flux is then reinjected into the image guide, emerges from it, reaches the scanning system, is then returned on the detection pathway by means of the separating plate, then focussed in a filtering hole. It is then detected for example by a photomultiplier or an avalanche photodiode. The signal originating from the photodetector is then integrated, then digitized in order to be displayed on a screen.
A device of this type is described in particular in International Patent Application WO 00/16151.
In the case of the analysis of a biological tissue, the difficulties that are encountered are linked to the low ratio of useful backscattered signal to parasitic signal, which, in order for the image produced to be acceptable, requires a quality of illumination beam which is the best possible and preserved throughout the optical path, in particular regarding the quality of the wave front and the spatial distribution of the focal spot intensity which must be as close as possible to the diameter of a fibre core. On the side of the proximal end of the image guide, the degradation of the illumination beam with respect to both energy and space is in particular due to the parasitic reflections occurring at the image guide input and to optical transmission faults at the scanning and injection systems (field deformation, wave front error).
In International Patent Application WO 00/16151 mentioned above, the scanning system comprises optomechanical resonating and/or galvanometric mirrors and the system for injecting into the image guide comprises a focusing lens L4 or microscope objective.